Defects of articular joints are significant sources of pain, discomfort and disability. These defects, such as full-thickness chondral defects, may be associated with osteoarthritis or other disease, traumatic injury and/or age or use-related degeneration of articular cartilage. Morbidity associated with defects of hyaline cartilage comprised by articular joints is responsible for significant economic, health and social costs.
The success of a tissue graft, for example a bone graft, in tissue repair is determined by its ability to recruit host cells to the site of the graft and modulate their conversion into the appropriate replacement tissue to repair the defect. For example, a bone graft relies on the ability of the graft to recruit osteoblasts and other bone-forming cells. This will depend on the osteoconductive, osteoinductive and osteogenic capabilities of the graft. Currently, autograft bone harvested from the iliac crest is considered the ‘gold standard’ due to its superior osteogenic properties. However, associated donor site morbidity, an increased surgery and recovery time, and a limited supply of donor bone are limiting its use. Allograft bone is a logical alternative to autograft. However, it must be rigorously processed and terminally sterilized prior to implantation to remove the risk of disease transmission or an immunological response. This processing removes the osteogenic and osteoinductive properties of the graft, leaving only an osteoconductive scaffold.
Current treatments for repair or amelioration of joint problems also include microfracture, abrasion and drilling to expose a joint containing a defect to mesenchymal stem cells. As a result of such interventions, the mesenchymal stem cells can infiltrate the defect, and differentiate into fibrocartilage over time. However, fibrocartilage has a structure and molecular composition distinct from that of the hyaline cartilage found in joints. The resulting fibrocartilage generally provides only short-term improvement, typically lasting less than two years. Alternative treatments are therefore needed.